Pvc blended with cross-linked graft co-polymer of styrene and methyl methacrylate onto a butadiene polymer

ABSTRACT

BUTADIENE-STYRENE-METHYLMETHACRYLATE COPOLYMERS PREPARED BY GRAFT-POLYMERIZATION WITH CROSS-LINKED BUTADIENE OR POLYBUTADIENE-STYRENE COPOLYMER LATEX OF STYRENE-METHYLMETHACRYLATE MONOMERS AND A CROSS-LINKING AGENT CAPABLE OF COPOLYMERIZING WITH SAID MONOMERS IN TWO STEPS. POLYVINYL CHLORIDE RESINS INCORPORATED WITH THE GRAFTCOPOLYMER EXHIBITS IMPROVED MECHANICAL STRENGTH AND OTHER PHYSICAL PROPERTIES.

United States Patent O 3,775,514 PVC BLENDED WITH CROSS-LINKED GRAFT C- POLYMER 0F STYRENE AND METHYL METH- ACRYLATE ONTO A BUTADIENE POLYMER Yasuo Amagi, Masaki Ohya, Zenya Shiiki, and Haruhiko Yusa, Iwaki, Japan, assignors to Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan No Drawing. Application Nov. 14, 1969, Ser. No. 876,920,

new Patent No. 3,671,610, which is a continuation-inpart of abandoned application Ser. No. 570,261, Aug. 4, 1966. Divided and this application Nov. 24, 1971, Ser. No. 201,978

Claims priority, application Japan, Aug. 9, 1965, ill/48,036; Feb. 5, 1966, ll/6,652, 41/6,653 Int. Cl. C08d 9/10 US. Cl. 260876 R 1 Claim ABSTRACT OF THE DISCLOSURE Butadiene-styrene-methylmethacrylate copolymers prepared by graft-polymerization with cross-linked butadiene or polybutadiene-styrene copolymer latex of styrene-methylmethacrylate monomers and a cross-linking agent capable of copolymerizing with said monomers in two steps.

Polyvinyl chloride resins incorporated with the graftcopolymer exhibits improved mechanical strength and other physical properties.

REFERENCE TO RELATED APPLICATION This application is a divisional application of Ser. No. 876,920 filed Nov. 14, 1969 now US. Pat. 3,671,610, which, in turn, is a continuation-in-part of our copending application Ser. No. 570,261 filed Aug. 4, 1966, now abandoned for Polymer Composition and Process for Producing the Same.

BACKGROUND OF INVENTION This invention relates to butadiene styrene methyl methacrylate graft-copolymers (hereinafter referred to as MBS resins). More particularly, the invention concerns a new MBS resin which, upon being mixed with a polyvinyl chloride or a copolymer containing a polyvinyl chloride as a principal constituent, is capable of imparting high transparency, impact resistance, and resistance to the stress whitening through bending to the resulting shaped articles of the composition.

Heretofore, the so-called graft copolymers produced by causing a post polymerization (or a consecutive polymerization which will hereinafter be denoted merely as polymerization) of vinyl monomers such as styrene, acrylonitrile, or methyl methacrylate either independently or as a mixture of a plurality thereof to a rubber-like polymer latex have been well-known.

These graft copolymers have good mechanical strength and have, therefore, been used independently for various shaped articles. In addition, these graft copolymers have been mixed with other resins such as polyvinyl chlorides to improve the impact resistance of shaped articles of these other resins.

However, most of the graft copolymers produced by hitherto known methods, while being capable of improving the impact resistance of polyvinyl chlorides when mixed and kneaded therewith, have been disadvantageous in that they produce products which are deficient in transparency and lack in resistance to the weathering. Particularly, resin compositions containing acrylonitrile as a constituent thereof has disadvantages such as low heat sta-- bility.

Furthermore, when shaped articles produced from these resins such as sheets, bottles, etc. are bent, the bent portions of the articles as well as the neighboring portions 3,775,514 Patented Nov. 27, 1973 thereof become extremely cloudy, whereby only products of low commercial value are obtained.

SUMMARY OF INVENTION It is therefore an object of the present invention to provide MBS resins which, upon being mixed and kneaded in minimal quantities with polyvinyl chloride, is capable of imparting to shaped articles formed from the resulting resin composition practically excellent properties such as high impact resistance, high transparency, resistance to weather, high heat stability, and almost no occurrence of the stress-whitening at bent portions of the products.

It is another object of the present invention to provide polyvinyl chloride resin composition produced by mixing and kneading polyvinyl chloride and the above-mentioned MBS resins manufactured for the above-mentioned particular purpose and exhibiting practically high impact resistance, high transparency, resistance to weather, high heat stability, and almost no occurrence of the stresswhitening at bent portions of products formed from such resin composition.

It is another object of the present invention to provide an improved method of producing cross-linked graft copolymer of butadiene-styrene-methyl methacrylate-divinyl compound having excellent properties in a relatively simple and economical manner.

The foregoing objects and other objects of the present invention will become more apparent from the following description of the invention when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING In the drawing, single figure is a graphical representation with triangular co-ordinates indicating the proportions of three constituent monomers of MBS resins according to the invention.

DETAILED DESCRIPTION OF INVENTION The MBS resins of the invention can be obtained, in general, by emulsion-polymerization of butadiene or a monomer mixture of butadiene as the principal constitucut and styrene, with addition of a small quantity of a cross-linking agent, to produce a polymer latex, causing a monomer mixture containing styrene and methyl methacrylate and a small quantity of a cross-linkaging agent as an additive to be adsorbed on the polymer latex and be polymerized thereon, or further adding thereto methyl methacrylate containing a cross-linking agent, and causing polymerization, and subjecting the latex thus obtained to salting-out, whereby BMS resin in the form of fine particles can be obtained.

By mixing from 5 to 20 parts by weight of an MBS resin obtained in this manner with from 95 to parts by weight of a polyvinyl chloride and forming shaped articles from the resulting resin, it is possible to produce products having the above-described excellent properties.

This MBS resin according to the invention may be considered to function in the following manner. When this MBS resin is mixed and kneaded with a polyvinyl chloride, rubber component particles of constant size are dispersed within the polyvinyl chloride in a form wherein they are protected by respective layers therearound of styrene-methyl methacrylate resin and methyl methacrylate resin. In this case, the styrene-methyl methacrylate layer is highly compatible with the rubber component, while the methyl methacrylate layer is highly compatible with the polyvinyl chloride. Moreover, as the plastic constituents in the respective latex particles thus graft-copolymerized are all crosslinked, the adhesion between the MBS particles is weak, whereby these particles can be readily dispersed within the polyvinyl chloride resin in a uniform manner. As a result, the transparency of the product is increased, and, at the same time, separation of the rubber-plastic phase and the polyvinyl chloride phase does not occur even at the time of bending the shaped articles, whereby stress-whitening also does not occur. The impact-resistance of polyvinyl chloride composition has heretofore been measured in accordance with ASTM D256-5 6 (Izod or Charpy impact strength values). However, as described at pages 199 to 206 of Modern Plastics, June 1956, the Izod impact strength test is to subject a notched test sample to destruction, hence the result will eventually be different from the actual strength of the shaped articles.

An important feature of the present invention is that the MBS resins obtained thereby are uniformly dispersed in solvents such as benzene, toluene, and tetralin and that the solution specific viscosity 17mm, (4 grams/litre, in benzene) thereof is within the range of from 0.01 to 0.06. The solution viscosity of an MBS resin obtained according to the invention decreases with increase in the degree of cross-linking and increases with decrease in the degree of cross-linking.

We have found that, while the shaped articles obtained by mixing and kneading of an MBS graft copolymer having a value of 1 lower than 0.01 and a polyvinyl chloride possess excellent transparency, but less effect of 'imparting impact resistance, when the value of nspJc, exceeds 0.06, the effect of imparting impact resistance increases, but particle dispersion becomes diflicult, and the transparency of the products is poor. Furthermore, the product is subject to a high degree of stress-whitening.

Many of the MBS resins or ABS resins (butadiene-styrene-acrylonitrile copolymers) produced by heretofore known methods are insoluble in solvents such as benzene, and those which are soluble have solution viscosities exceeding 0.1. These MBS resins and ABS resins have a further disadvantage in that shaped articles produced by kneaded mixtures of these resins with polyvinyl chlorides do not have very good transparency.

Through consideration of these disadvantageous features of these resins obtained by known methods, we have discovered that there exists a close interrelationship between the solution viscosity and transparency as well as the stress-whitening of MBS resins, as described more fully hereinafter.

A further feature of the present invention is that the index of refraction of the MBS graft copolymer produced thereby is within the range of from 1.528 to 1.540. That is, the indexes of refraction of polyvinyl chlorides and copolymers with vinyl chloride as their principal constituents are from 1.530 to 1.538 at 20 degrees C., and it is important that the indexes of refraction of the MBS resins to be admixed therewith coincide almost exactly with these values. If the index of refraction is outside of the abovestated range, the resulting shaped article will become nontransparent or in some cases produce scattered light of strong purple colour.

The indexes of refraction 11 at 20 degrees C. of polymers of butadiene, methyl methacrylate, and styrene are 1.515, 1.494, and 1.590, respectively, and in the case of the polymers according to the invention, it may be considered that the additive property (or additivity rule) due to the weight composition is approximately realized.

As shown in the graphical representation of the accompanying drawing, when the entire composition of a resin is contained within the region bounded by the reference letters ABCDEF, and, at the same time, the resin possesses a value of 1 within the above specified range, mixing and kneading of the resin with a polyvinyl chloride produces a transparent shaped article.

More specifically, it is requisite that the composition of the three monomers be from 24 to 60 percent of butadiene, from 22 to 43 percent of styrene, and from 5 to 46 percent of methyl methacrylate.

A further important feature of the MBS resins according to the invention is the compositional ratio of the ru b r on tu t and th p stics cqn tituent- 0t cour e.

if only impact resistance were to be considered as a problem, as large a rubber content as possible would be desirable, but if the rubber content is increased to an extreme degree, agglomeration or lumping will result from steps such as salting-out and drying, or the mixing and kneading with the polyvinyl chloride will be made difficult, and as a result uniform dispersion cannot be attalned.

On the other hand, in the case where the rubber content is below 40 weight percent, the effect of imparting impact resistance is small, and the other physical properties of polyvinyl chloride such as heat and temperature resistance and gas impermeability becomes deficient. That is, the compositional ratio by weight of the rubber constituent and the plastics constituent is preferably in the range of (40 to parts by weight of rubber: (60 to 25) parts by weight of plastics.

For the rubber constituent, a butadiene polymer or a butadiene styrene copolymer which has or has not been cross-linked is used. It has been found that in the case of a butadiene styrene copolymer, a styrene content of 40 weight percent or less produces excellent results.

For the plastics constituent, a polymer produced by causing a monomer mixture of styrene and methyl methacrylate containing a cross-linking agent to be adsorbed and polymerized on rubber latex particles is used. It has been found that the styrene content in the monomer mixture is preferably in the range of from 40 to weight percent.

In this case, it has been found that, rather than the plastics constituent of a specific quantity be polymerized in one step on the rubber constituent, it is preferable to resort to a two-step graft-polymerization process in which the plastics constituent is divided into two parts, and which comprises carrying out a first graft-polymerization step, adding a monomer mixture of styrene and a part of methyl methacrylate containing a cross-linking agent upon completion of the greater part of the first graft-polymerization step, and subsequently carrying out a second graftpolymeriaztion step by adding the remainder portion of methyl methacrylate.

This two-step method has the effect of further improving the properties of the blending of the MBS resin produced with the polyvinyl chloride and increasing the rate dispersion into the polyvinyl chloride. Furthermore, compatibility of the MBS resins and the polyvinyl chloride increases and the stress-whitening through bending is improved.

The quantity of MMA monomer polymerized in the second step is preferably from 10 to by weight to the total methyl methacrylate. Furthermore, even in the case where the graft-polymerization of the plastics constituent with respect to the rubber constituent is carried out in two steps, the cross-linking agent should be added in both the first and second steps.

The cross-linking agent to be added to the rubber component or graft component according to the invention is selected from among those which copolymerize well with styrene, butadiene, and methyl methacrylate. Examples of suitable cross-linking agents are divinyl benzene and dimethacrylates such as mono-, di-, tri-, or tetra-ethylene glycol dimethacrylate and 1,3-butylene glycol dimethacrylate. The quantity of the cross-linking agent used is from 0.01 to 5 weight percent of the total quantity of the monomers which exist in the copolymers.

The polyvinyl chlorides suitable for use according to the invention are those obtainable by various known methods such as emulsion-polymerization and suspensionpolymerization. In addition to independent polymers, it is also possible to use a copolymer consisting of 70 percent or more of vinyl chloride and other monomers to be copolymerized therewith such as mono-olefin monomers, e.g., vinyl acetate, acrylonitrile, vinylidene chloride, alkyl vinyl ether, etc. or mixtures thereof. From 5 to 20 parts by weight of a resin obtained according to the invention is mixed with from 95 to 80 percent by weight of a polyvinyl chloride of the above stated character.

While it is possible to carry out the mixing, in general, with the materials in powder form by means of apparatus such as a roll mill or a Banbury type mixer, it is also elevated temperature of 60 degrees C. and caused to react for 5 hours.

The latex thus obtained was salted-out at 50 degrees C. with a I-percent salt solution, further heat-treated at 80 C., and filtered. The powder particles filtered out were 5 possible to m1x the latex obtained and the polyvinyl chlowashed with water and then dried, whereupon an MBS r1de latex and then to subject the resulting mixture to resin of 1 value of 0.032 was obtained with a yield salting-out or spray drying thereby to produce a mixed of 98.5 percent. resln composinon. 13 parts of this resin was mixed with 87 parts of a poly- As descnbed above, the MBS resins according to the vinyl chloride of a polymerization degree of 800 containmvention, when mlxed with polyvinyl chlorides, impart ing 2 parts of dibutyl-tin-dilaurate, and the resulting mixexcellent transparency and impact resistance to the shaped ture was roll-kneaded at 140 degrees C. for 4 minutes articles formed from the resulting mixture resins. The and then pressed at 190 degrees C. under a pressure of use of these MBS resins, however, is not limited to only 100 kg./cm. into a sheet of 3 mm. thickness. that for mixing with polyvinyl chlorides, these MBS resins The Charpy impact strength of this sheet as tested on being useful also for mixing with other resins as, for a notched test piece according to ASTM D-256-56 was example, chlorinated polyvinyl chloride and vinylidene 85 kg. cm./cm. The light transmittance of the sheet chloride copolymers thereby to increase their impact-reaccording to ASTM D-1003-52 was 81.5 percent, and sistant strength. the haze value was 3.5 percent. Furthermore, when a sheet of l-mm. thickness of the same resin was bent PREFERRED EMBODIMENTS through 180 degrees C. at C., clouding was observed In order to indicate still more fully the nature and to be extremely less. utility of the present invention, the following examples In addition, when a mixture of 0.1 part of calcium of practice thereof are set forth, it being understood that stearate, 0- P Of Zinc Stearate, and 6 P of an P these examples are presented as being illustrative only, 25 compound of soybean oil was used in place of the above and that they are not intended to limit the scope of the described stabilizing agent, and bottles, each of 530 cc. invention. capacity and 25-grams weight, were formed by means Example 1 of an extruding machine, bottles of excellent transparency were obtained very easily.

lohtre stamless'steel autoclave prqvlded Wlth an Fifty of these bottles were cooled to 5 degrees C., filled asltator was F f under a vacuum Wlth a monomer with water, and subjected to repeated free drop tests from mlxture consistmg of 1 gram of cumene hydropero a height of 1 metre until breakage occurred. As a result, (CHP), 800 grams of butadlene, grams of Styrene the average number of drops for breakage was 29 drops. and 5 grams of meihlflene glycol dlmelhicrylate (DMA) For comparison, a similar test was carried out with simand of dlslllled Water contammg 10 of ilar bottles produced from only a polyvinyl chloride, in Nablsoctyl sulfosuccmate, gram of EDTA'fhsodlum which case the average result was 2 drops for breakage. mono-hydnde, 0.05 gram of formaldehyde sodium sulfoxylate (Rongalite), 0.03 gram of ferrous sulphide, and Example 2 gram of Sodium PY P P The mammals thus The process as set forth in Example 1 was followed excharged were then caused to react at degrees C. f0! 40 gept that the degree of cross-linking was changed, and approximately 17 hours, at Whlch tlme no further Pressure I the methyl methacrylate to be added in the second step drop was observable. was added in the first step. Representative examples re- Next, to the resulting charge, a monomer mixture of lating to the resulting products are indicated in the accom- 300 grams of styrene containing 0.5 gram of CHP and panying Table I.

TABLE 1 Rubber constituent (parts Plastics constituent (parts by weight) ot- Number Anti-stressby weight) of- Impact of repeated whitening Methyl Meth 1 resistance drops (500 Transproperty Buta- Sty- Stymethmet se ec., 25 g. parency, through Sample diene rene DMA rene acrylate DMA acrylate DMA n.,,.[.,. (percent) bottle) percent bending (Invention) A 40 10 0.25 15 20 0.175 0 0 0. 045 13 20 79.0 Good. 13.- 40 10 0.25 15 10 0.850 10 0.3 0. 01a 15 19 83.5 Excellent. 0-- 4o 10 0.25 15 10 0.500 10 0.2 0.020 13 22 83.2 D0. 1).. 40 10 0.25 15 10 0.30 10 0.1 0.025 12 25 82.2 D0. E 40 10 0.25 15 10 0.15 10 0.05 0.032 11 29 21.5 Do. (Comparative samples):

40 10 0 15 10 0 10 0 0.080 10 9 57.0 Poor. 40 10 0.25 15 10 0 10 0 0.065 11 10 68.3 Do. 40 10 0.00 15 10 0 10 0 0.048 11 9 72.2 Do. 40 10 1.20 15 10 0 10 0 0.035 12 s 75.4 Do.

1 DMA=Triethylene-glycoldimethacrylate. 1 Charpy impact strength tests were earned out on notched test pieces 0f resins with varying blend proportions, and the point of transition from brittle fracture t0 ductile fracture was taken in each case.

Example 3 50 parts by weight of rubber constituent obtained in exactly same manner as set forth in Example 1 was graftpolymerized with 35 parts by weight of styrene and methyl methacrylate monomer mixtures, in which the methyl methacrylate was divided into two parts in accordance with the ratio shown in the following Table 2 and added to the rubber constituent in two separate steps. The solution viscosity and physical properties of the PVC 30 minutes. Thereafter, the batch was maintained at an shaped articles are shown in Table 2.

TABLE 2 Plastics constituent (parts by weight) oi- Rubbcr constituent Number of Anti-stress- (parts by weight) oi Metliyl- Methyl- Impact repeated whitening; methmethresistdrops (600 'lrausproperty Buta- Sty- Styacryacryauce rise cc., 25 g. parency through Sample diene rene DMA rene late DMA late DMA 1sp./c. (percent) bottle) (percent) bending 40 10 0. 25 15 20 0. 175 0 0. 045 13 20 l 79. 0 Good. 40 10 0. 25 15 15 0. 175 0. 025 0. 032 12 22 l 80. 5 Excellent. 40 O. 25 10 0. 150 10 0. 05 0. 032 11 29 1 81. 5 D0. 40 10 0. 25 15 6 0. 125 15 0. 075 O. 033 13 27 1 81. 5 D0. 40 10 Y 0. 25 15 2 1 0.120 18 1 0. 080 0. 033 15 15 1 81. 0 Do. 40 10 0. 25 15 1O 0. 150 10 O. 05 0. 028 12 28 l 82. 0 Do.

1 Glass clear. 2 DVB: Divinyl-benzeno.

Example 4 As seen from Table 4 above, in case the rubber content 50 parts by weight of the rubber constituent obtained 15 large (sample good result can be otftamed in exactly same manner as set forth in Example 1 was when the shaped aftlcle is Subjected to 'PY Impact graftpolymerized with 35 parts by weight of styrene and strength test, though the actual destruction resistance methyl methacrylate monomer miXture at a ratio as indithereof is poor and its anti-stress-whitening property is cated in the following Table 3, in which the methyl methalso inferior. This is due to the fact that, as the rubber acrylate is divided into two parts and added to the rubber constituent in two separate Steps. content in the resin thus obtained is high, the resin is The solution viscosity and physical properties of PVC prone to coagulate at the time of salting'out which Preshaped articles obtained in the same manner as in Exam- Vents 1t 0111 dlsperslng Perfectly 1n the p y y Chlorideple 1 are shown in Table 3. On the other hand, when the rubber content is small TABLE 3 Plastics constituent (parts by'weight) 01- Number of Anti- Rubber constituent Impact repeated stress- (parts by weight) of- Methyl- Methylresistdrops whitening methmethance (500 (20., Transproperty Buta- Sty- Styacryacryrise g. parency through Sample diene rene DMA rene late DMA late DMA mole. (percent) bottle) (percent) bending 40 10 0. 25 5 2O 0. 15 10 O. 05 0. 031 12 10 2 70. 0 Excellent. 40 10 0. 25 10 15 0. 15 10 0. 05 0. 032 13 15 2 75. 0 Do. 40 10 0. 25 15 10 0. 15 10 0. 05 0. 032 11 29 5 81. 5 D0. 40 1O 0. 25 20 5 0. 15 1O 0. 05 O. 031 13 22 3 80. 5 GOOd. 40 10 0.25 2 0. 3 0. 05 0.032 12 8 4 65. 0 Poor.

1 Samples N, O, and Q are presented for comparison purposes, in which 2 Strong yellow. N and 0 indicate the cases where the amount of Styrene is extremely Glass clear. small, and Q indicates the case where the amount oi MMA is extremely 4 Strong blue. sma

As seen from Table 3 above, when the quantity of (Sample No. S), the impact resistance thereof deteriorates styrene in the rubber constituent is small (Sample Nos. extremely.

N and O), the obtained article assumes strong yellow and What we claim is:

possesses poor transparency. On the contrary, when the 1. A polyvinyl chloride resin composition having imquantity of styrene is large, the shaped product assumes proved transparency, impact resistance, anti-stress-whitenstrongblue, is non-transparent, and poor 1n antlres ing through bending which consists of from 95 to 80 whitening through bending In order therefore to obta1n parts by weight of polyvinyl chloride, and from 5 to 20 thefihaped P f- Satlsfylng the deslred Propertles, the parts by weight of a graft copolymer of butadiene, styrene optimum blending rate of styrene and methyl methacryand methylmethacrylate said graft Co 01 mar bein l 5O P y g P ate is -80% by weight of styrene and -20% by duced by the Steps of:

welght of methyl methacrylate' (a) preparing a latex of a butadiene polymer by polym- Example 5 erizing a monomer selected from the group consist- 50 parts by weight of rubber constituent obtained n r mg of buiadlene a a mlxturof, butadlen? and exactly same manner as set forth in Example 1 was gram 5o styrene with butadiene as the principal constituent polymerized with varying blend rate of styrene and meth- Presence a Small quanmy of a Y Y Cross yl methacrylate monomer mixture and resins respectively lll'lklng agent, 531d p y latex Contalnlng from containing 80, 59, and 38% of the rubber constituent 40 to Parts y weight of said butadlene p y were obtained as shown in Table 4 below. (b) adding to said latex from 60 to 25 parts by weight The solution viscosity and physical properties of PVC 60 of styrene and methylmethacrylate monomers at a shaped article obtained in accordance with Example 1 ratio of 40 to parts by weight of styrene to 60 to are shown in Table 4. 20 parts by weight of methylmethacrylate, and a TABLE 4 Plastics constituent (parts by weight) ei- Number of Anti- Rubber constituent Impact repeated stress- (parts by Weight) oi- Methyl- Methylresistdrops whitening v methmeth- Rubber ance (500 00., Transproperty Buta- Sty- Styacryaerycontent rise 25g. parency through Sample diene rene DMA rcne late DMA late DMA (percent) lupJc. (percent) bottle) (percent) bending 40 10 0.25 5.5 35 0. 054 3.5 0.0175 80 0.029 s 12 77.0 Poor. 40 10 0.25 15 10 0.15 10 0.05 59 0.032 11 29 81.5 Excellent. 40 10 0.25 35 23 0.35 23 0.115 38 0.036 18 5 79.0 Do.

1 Samples R and S are presented for comparison purpose. I Slight yellow. P Glass clear.

small quantity of a divinyl cross-linking agent copolymerizable with said monomer,

(1) said methylmethacrylate being divided into two portions, from 10 to 90 percent by weight of which is added to the latex together with said 40 to 80 parts by weight of styrene in the first stage graft polymerization;

(2) the remainder portion of which is added singly to the latex in the second stage graft-polymerization, when a greater part of the first polymerization step is completed,

(3) the quantity of said cross-linking agent being in the range of from 0.01 to 5 percent by Weight of the total quantity of the monomers existing in the copolymer and being present in each monomer portion; and

(c) reacting the mixture to form said graft copolymer.

10 References Cited UNITED STATES PATENTS 3,328,488 6/1967 Delacretaz et a1 260880 3,288,886 11/1966 Himei et a1 260-876 5 3,651,177 3/1972 Saito et 1 260876 2,943,074 6/1960 Feuer 260-876 X FOREIGN PATENTS 10 994,924 6/1965 Great Britain 260-876 MURRAY TILLMAN, Primary Examiner J. SEIBERT, Assistant Examiner US. Cl. X.R.

15 26023.7 R, 29.7 UA, 29.7 UP, 45.75 K, 45.85, 45.8 A, 

